Microtubules in Asgard archaea
Florian Wollweber1,3 ∙ Jingwei Xu (许靖蔚)1,3 ∙ Rafael I. Ponce-Toledo2,4∙ … ∙ Michal Wieczorek1 ∙ Christa Schleper2 ∙ Martin Pilhofer1,5
Highlights
• Asgard archaea express tubulins related to eukaryotic α/β-tubulin and bacterial BtubA/B
• Asgard tubulins (AtubA/B/B2) assemble into canonical and non-canonical heterodimers
• Asgard tubulin heterodimers polymerize into 5 or 7 protofilament microtubules
• AtubA/B form cytoskeletal structures in Ca. Lokiarchaeum ossiferum
Summary
Microtubules are a hallmark of eukaryotes. Archaeal and bacterial homologs of tubulins typically form homopolymers and non-tubular superstructures. The origin of heterodimeric tubulins assembling into microtubules remains unclear.
Here, we report the discovery of microtubule-forming tubulins in Asgard archaea, the closest known relatives of eukaryotes. These Asgard tubulins (AtubA/B) are closely related to eukaryotic α/β-tubulins and the enigmatic bacterial tubulins BtubA/B. Proteomics of Candidatus Lokiarchaeum ossiferum showed that AtubA/B were highly expressed. Cryoelectron microscopy structures demonstrate that AtubA/B form eukaryote-like heterodimers, which assembled into 5-protofilament bona fide microtubules in vitro. The additional paralog AtubB2 lacks a nucleotide-binding site and competitively displaced AtubB. These AtubA/B2 heterodimers polymerized into 7-protofilament non-canonical microtubules. In a sub-population of Ca. Lokiarchaeum ossiferum cells, cryo-tomography revealed tubular structures, while expansion microscopy identified AtubA/B cytoskeletal assemblies.
Our findings suggest a pre-eukaryotic origin of microtubules and provide a framework for understanding the fundamental principles of microtubule assembly.
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